It looks like you may have something very special. Here is the reply from our second source, another long time reenactor with a lifetime of studying this era under his belt:
"Oh my god. The Army came out with an experimental combination meat ration can and coffee tin cup in the 1870s. Imagine drinking coffee out of a bacon grease-soaked tin cup. It was a prototype that the troops hated and was short-lived. I'll get more details when I get home tomorrow."